Method and system for calibrating group delay errors in a combined gps and glonass receiver

ABSTRACT

A combined GPS and GLONASS receiver receives GPS signals and GLONASS signals. A calibration signal is generated utilizing the received GPS signals and/or the received GLONASS signals to offset group delay errors in the received GLONASS signals. The generated calibration signal is filtered through Kalman filters to estimate group delay variations in the received GLONASS signals. The estimated group error delay variations are combined with the received GLONASS signals to calibrate the received GLONASS signals by offsetting the estimated group error delay variations. When GPS signals are not available for use, the combined GPS and GLONASS receiver obtains group delay errors stored or in the received GLONASS signals to estimate calibration coefficients. The estimate calibration coefficients are updated utilizing received GPS and/or GLONASS signals. The updated estimated calibration coefficients are stored before turning off the combined GPS and GLONASS receiver to expedite calibrating of GLONASS signals received upon turning on.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation in part of U.S. application Ser. No.12/192,963 filed on Aug. 15, 2008, and makes reference to, claimspriority to, and claims the benefit of application Ser. No. 12/192,963filed on Aug. 15, 2008.

The above state application is hereby incorporated herein by referencein its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to signal processing fornavigation satellite systems (NSS). More specifically, certainembodiments of the invention relate to a method and system forcalibrating group delay errors in a combined GPS and GLONASS receiver.

BACKGROUND OF THE INVENTION

The Global Positioning System (GPS) and the Global Orbiting NavigationSatellite System (GLONASS) are two Global Navigation Satellite Systems(GNSS). GNSS receivers may normally determine their position byreceiving satellite broadcast signals from a plurality of satellites.

A fully operational GPS comprises up to 24 earth orbiting satellitesapproximately uniformly dispersed around six circular orbits with foursatellites each. Each satellite carries a cesium or rubidium atomicclock to provide timing information for the signals transmitted by thesatellites. Each GPS satellite transmits L-band carrier signalscontinuously in two frequency bands centered at 1575.42 MHz and 1227.6MHz, denoted as L1 and L2 respectively. The GPS L1 signal isquadri-phase modulated by two pseudo-random noise (PRN) codes in phasequadrature, designated as a coarse/acquisition code (“C/A code”) and aprecision ranging code (“P-code”). The GPS L2 signal is BPSK modulatedby only the P-code. The C/A code is a gold code that is specific to eachsatellite, and has a symbol rate of 1.023 MHz. The unique content ofeach GPS satellite's C/A code is used to identify the source of areceived signal. The P-code, is a relatively long, fine-grained codehaving an associated clock or chip rate of 10 f0=10.23 MHz. The fullP-code has a length of 259 days, with each satellite transmitting aunique portion of the full P-code. The portion of the P-code used for agiven GPS satellite has, a length of precisely one week (7.000 days)before this code portion repeats. The GPS satellite signals comprisenavigational information of the transmitting GPS satellite which may beexploited by a corresponding satellite receiver to determine its ownnavigation information such as the satellite receiver's position andvelocity.

The GLONASS system uses 24 satellites, distributed approximatelyuniformly in three orbital planes of eight satellites each. The GLONASSsystem transmits L-band carrier signals continuously in two frequencybands, denoted as L1 and L2, respectively, centered at frequencies off1=(1.602+9k/16) GHz and f2=(1.246+7k/16) GHz, where k (=1, 2, . . . 24)is the channel or satellite number. Each GLONASS satellite transmitssignals in frequencies that are specific to each satellite. The GLONASSL1 signal is modulated by a C/A-code with a chip rate=0.511 MHz and by aP-code with a chip rate=5.11 MHz). The GLONASS L2 signal is BPSKmodulated by only the P-code. The P-code is the same, and the C/A-codeis the same, for each GLONASS satellite. The GLONASS satellite signalscomprise navigation information of the transmitting GLONASS satellitewhich may be exploited by a corresponding satellite receiver todetermine its own navigation information such as the satellitereceiver's position and velocity.

Both the GPS system and the GLONASS system use transmission of codedradio signals, with the structure described above, from a plurality ofEarth-orbiting satellites. Further limitations and disadvantages ofconventional and traditional approaches will become apparent to one ofskill in the art, through comparison of such systems with some aspectsof the present invention as set forth in the remainder of the presentapplication with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A method and/or system for calibrating group delay errors in a combinedGPS and GLONASS receiver, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating an exemplary satellite navigationsystem, in accordance with an embodiment of the invention.

FIG. 2 is a diagram illustrating an exemplary combined GPS and GLONASSreceiver, in accordance with an embodiment of the invention.

FIG. 3 is a diagram illustrating an exemplary calibration signalgenerator, in accordance with an embodiment of the invention.

FIG. 4 is a diagram illustrating an exemplary error state Kalman filterused in a combined GPS and GLONASS receiver, in accordance with anembodiment of the invention.

FIG. 5 is a flow chart illustrating exemplary steps for calibratinggroup delay errors in a combined GPS and GLONASS receiver, in accordancewith an embodiment of the invention.

FIG. 6 is a flow chart illustrating exemplary steps for offsetting groupdelay errors in a combined GPS and GLONASS receiver, in accordance withan embodiment of the invention.

FIG. 7 is a flow chart illustrating exemplary steps for immediatelyoffsetting group delay errors in a combined GPS and GLONASS receiverupon turning on, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor calibrating group delay errors in a combined GPS and GLONASSreceiver. Various aspects of the invention may provide calibratingreceived GLONASS signals based on a GPS based navigation for a combinedGPS and GLONASS receiver. The combined GPS and GLONASS receiver mayreceive a plurality of GPS signals and a plurality of GLONASS signals. Acalibration signal may be generated utilizing the received GPS signalsand/or the received GLONASS signals. The generated calibration signalmay be utilized to offset group delay errors in one or more of theplurality of received GLONASS signals. The generated calibration signalmay be processed or filtered through one or more Kalman filters beforethe calibration of the received GLONASS signals occurs. The filteredcalibration signal may be utilized to offset the group delay errors inthe received GLONASS signals. The filtered calibration signal isreflective of the group delay variations associated with the receivedGLONASS signals. The group delay variations may be estimated via theKalman filtering. The estimated group delay variations may be combinedwith the received GLONASS signals to calibrate the received GLONASSsignals by offsetting the estimated group delay variations in thereceived GLONASS signals. The resulting calibrated received GLONASSsignals may be utilized to generate GLONASS related navigationinformation. In instances where the estimated group delay variations arestable, the received GLONASS signals may also be directly applied orutilized by the combined GPS and GLONASS receiver to generate GLONASSrelated navigation information.

In some circumstances, the combined GPS and GLONASS receiver may receivethe GLONASS signals before the presence of the GPS signals. In thisregard, the combined GPS and GLONASS receiver may start the estimationof the group delay variations in the received GLONASS signals before theGPS signals become available for use. For example, the combined GPS andGLONASS receiver may obtain or collect group delay errors from thereceived GLONASS signals to estimate the group delay variations in thereceived GLONASS signals. The combined GPS and GLONASS receiver may alsoobtain or utilize group delay errors previously stored inside thecombined GPS and GLONASS receiver to estimate the group delay variationsin the received GLONASS signals. The estimated group delay variationsmay be utilized as calibration coefficients to generate the calibrationsignal. The combined GPS and GLONASS receiver may utilize the generatedcalibration signal to offset the group delay errors in the receivedGLONASS signals. Once the GPS signals are received or become availablefor use, the estimated group delay variations may be updated utilizingthe received GPS signals. The updated group delay variations may then beutilized to generate an updated calibration signal to offset the groupdelay errors in the received GLONASS signals. The updated group delayvariations may be stored before turning off the combined GPS and GLONASSreceiver, and may be utilized to generate a newly updated calibrationsignal for the calibration of GLONASS signals received upon turning onthe combined GPS and GLONASS receiver.

FIG. 1 is a diagram illustrating an exemplary satellite navigationsystem, in accordance with an embodiment of the invention. Referring toFIG. 1, there is shown a satellite navigation system 100, comprising acombined GPS and GLONASS receiver 120, a GPS receiver 140, a GLONASSreceiver 160, and a plurality of satellites, of which satellites 110 a,110 b, 110 c, and 110 d may be illustrated. The combined GPS and GLONASSreceiver 120, the GPS receiver 140, and the GLONASS receiver 160 may becommunicatively coupled to a receiver antenna 130, a receiver antenna150, and a receiver antenna 170, respectively.

The satellites 110 a through 110 d may comprise suitable logic,circuitry and/or code that may be enabled to generate and broadcastsuitable radio-frequency (RF) signals that may be received by asatellite receiver, for example, the combined GPS and GLONASS receiver120, and the GPS receiver 140, and the GLONASS receiver 160. Thegenerated broadcast RF signals may be utilized to determine navigationinformation such as, for example, the position, the velocity, and theclock information of the combined GPS and GLONASS receiver 120, the GPSreceiver 140 and/or the GLONASS receiver 160.

The combined GPS and GLONASS receiver 120 may comprise suitable logic,circuitry and/or code that may be enabled to receive signals broadcastedfrom both GPS and/or GLONASS satellites, for example, the satellites 110a through 110 d. The combined GPS and GLONASS receiver 120 may beenabled to process the received satellite signals to identify thesatellite source for each satellite signal, determine the time at whicheach identified satellite signal arrives at the antenna 130, anddetermine the present location of the satellite source such as thesatellites 110 a, 110 b, 110 c, or 110 d. The combined GPS and GLONASSreceiver 120 may be capable of tracking a plurality of both the GPSsatellites and the GLONASS satellites and take measurements of code andcarrier phase from each satellite. The received signals, whether GPS orGLONASS, may be processed by the combined GPS and GLONASS receiver 120to provide navigation information. The navigation information may becalculated based on the received GPS signals, and/or the receivedGLONASS signals. Errors such as the group delay error in the receivedGLONASS signals may be removed or offset based on the GPS basednavigation information while maintaining the combined GPS and GLONASSreceiver 120 with the specific desirable characteristics such asanti-jamming capabilities. The combined GPS and GLONASS receiver 120 mayoperate with an initial assumption that the group delay errors for eachGLONASS frequency band maybe unknown and as a result, may rely solely onthe received GPS signals. Once a fix has been obtained on a transmittingGPS satellite, computed GPS navigation information may be used todetermine the expected GLONASS signals.

In some circumstances, the combined GPS and GLONASS receiver 120 mayreceive GLONASS signals before GPS signals are present or received. Thecombined GPS and GLONASS receiver 120 may learn or obtain group delayerrors in the received GLONASS signals so as to estimate group delayvariations associated with the received GLONASS signals. The estimatedgroup delay variations may be utilized to offset or remove the groupdelay errors in the received GLONASS signals.

In some instances, group delay variations and/or group delay errors inGLONASS system may be previously stored inside the combined GPS andGLONASS receiver 120. In this regard, before GPS signals becomeavailable for use, the combined GPS and GLONASS receiver 120 may utilizethe stored group delay variations to offset the group delay errors inthe received GLONASS signals. The combined GPS and GLONASS receiver 120may also estimate group delay variations utilizing the stored groupdelay errors to offset the group delay errors in the received GLONASSsignals. Once GPS signals are present or become available for use, thecombined GPS and GLONASS receiver 120 may incorporate the GPS signals tocalibrate the received GLONASS signals by offsetting the associatedgroup delay errors. For example, the combined GPS and GLONASS receiver120 may derive or compute GPS navigation information from the GPSsignals. The computed GPS navigation information may be converted ortransformed into corresponding GLONASS navigation information, which maybe utilized by the combined GPS and GLONASS receiver 120 to estimategroup delay variations and/or group delay errors in the received GLONASSsignals. The resulting estimated group delay variations and/or groupdelay errors may then be utilized to offset the group delay errors inthe received GLONASS signals.

In some circumstances, the combined GPS and GLONASS receiver 120 mayneed to be turned off or shut down. The combined GPS and GLONASSreceiver 120 may store the latest group delay variations and/or groupdelay errors before turning off. The combined GPS and GLONASS receiver120, upon turning on, may utilize the stored group delay variationsand/or group delay errors to immediately start the calibration ofGLONASS signals received. The stored group delay variations and/or groupdelay errors may be updated or refined dynamically utilizing GPS signalsand/or GLONASS signals received after the combined GPS and GLONASSreceiver 120 is turned on. The combined GPS and GLONASS receiver 120 mayincorporate or utilize the updated group delay variations and/or groupdelay errors to continue the calibration of the received GLONASSsignals.

The antenna 130 may comprise suitable logic, circuitry and/or code thatmay be enabled to receive L band signals from a plurality of GPSsatellites and a plurality of GLONASS satellites and pass to thecombined GPS and GLONASS receiver 120 to be processed for correspondingnavigation information. Although a single antenna 130 is illustrated,the invention may not be so limited. Accordingly, one or more antennasmay be utilized by the combined GPS and GLONASS receiver 120 withoutdeparting from the spirit and scope of various embodiments of theinvention.

The GPS receiver 140 may comprise suitable logic, circuitry and/or codethat may be operable to receive signals broadcasted from GPS satellites,for example, the satellites 110 a. The GPS receiver 140 may be enabledto process the received satellite signals to identify the satellitesource for each satellite signal, and determine the time at which eachidentified satellite signal arrives at the antenna 150. The GPS receiver140 may also be operable to determine a present location of thesatellite source such as the satellites 110 a and 110 b. The GPSreceiver 140 may be capable of tracking a plurality of the GPSsatellites and may take measurements of code and/or carrier phase fromeach GPS satellite. The received GPS signals may be processed by the GPSreceiver 140 to provide navigation information. The navigationinformation may be calculated based on the received GPS signals.

The antenna 150 may comprise suitable logic, circuitry and/or code thatmay be enabled to receive L band signals from a plurality of GPSsatellites and communicate them to the GPS receiver 140 where they maybe processed to generate corresponding navigation information.

The GLONASS receiver 160 may comprise suitable logic, circuitry and/orcode that may be operable to receive signals broadcasted from GLONASSsatellites, for example, the satellites 110 c. The GLONASS receiver 160may be enabled to process the received satellite signals to identify thesatellite source for each satellite signal, determine the time at whicheach identified satellite signal arrives at the antenna 170, anddetermine the present location of the satellite source such as thesatellites 110 c and 110 d. The GLONASS receiver 160 may be capable oftracking a plurality of the GLONASS satellites and may take measurementsof code and/or carrier phase from each GLONASS satellite. The receivedGLONASS signals may be processed by the GLONASS receiver 160 to providenavigation information. The navigation information may be determinedbased on the received GLONASS signals.

The antenna 170 may comprise suitable logic, circuitry and/or code thatmay be enabled to receive L band signals from a plurality of GLONASSsatellites and communicate them to the GLONASS receiver 160 where theymay be processed to generate corresponding navigation information.

In operation, the combined GPS and GLONASS receiver 120 may receive aplurality of satellite signals from GPS satellites such as 110 a and 110b, and GLONASS satellites such as 110 c and 110 d. The combined GPS andGLONASS receiver 120 may be enabled to identify the satellite source foreach satellite signal. For example, each GLONASS satellite may beidentified by its satellite vehicle identification number (SV.sub.--ID)acquired from the GLONASS almanac data which may be related to thecarrier transmission frequency of a particular GLONASS satellite. EachGPS satellite may be identified by matching or correlating a uniqueportion of the GPS P-code for that particular satellite. Once asynchronization or lock has been successfully established on thetransmitting GPS satellites and GLONAS satellites, the combined GPS andGLONASS receiver 120 may take code and carrier phase measurements oneach identified satellite signals, GPS and/or GLONASS, received via theantenna 130.

The combined GPS and GLONASS receiver 120 may be operable to process thereceived GPS signals and generate GPS navigation information for thecombined GPS and GLONASS receiver 120. Respective GLONASS signals may beestimated based on the GPS navigation information and a calibrationsignal. The calibration signal may be reflective of group delayvariations associated with the received GLONASS signals. The calibrationsignal may be derived or generated based on a comparison of theestimated GLONASS signal and actual received GLONASS signals. Thecalibration signal may be used to calibrate the received GLONASS signalsby offsetting or removing associated group delay errors. GLONASS basednavigation information may be calculated based on the calibrated GLONASSsignals. The combined GPS and GLONASS receiver 120 may operable togenerate the GPS based navigation information, the GLONASS basednavigation information, and/or a combined version of the GPS navigationinformation and the GLONASS navigation information.

In instances where the combined GPS and GLONASS receiver 120 receivesGLONASS signals before GPS signals are present, the combined GPS andGLONASS receiver 120 may start the calibration of the received GLONASSsignals. For example, in instances where group delay variations and/orgroup delay errors for GLONASS channels may be previously stored intothe combined GPS and GLONASS receiver 120 by manufacturer and/orreceiver designers, the combined GPS and GLONASS receiver 120 mayutilize the stored group delay variations and/or group delay errors togenerate a calibration signal. The generated calibration signal may beutilized to offset or remove the group delay errors in the receivedGLONASS signals.

In another exemplary embodiment of the invention, the combined GPS andGLONASS receiver 120 may be operable to process or filter the receivedGLONASS signals to generate or determine GLONASS navigation informationfor the combined GPS and GLONASS receiver 120. The combined GPS andGLONASS receiver 120 may learn or obtain or otherwise determine thegroup delay errors in the received GLONASS signals via the generatedGLONASS navigation information. Group delay variations may be determinedand may be utilized as calibration coefficients to form or generate acalibration signal. The combined GPS and GLONASS receiver 120 mayutilize the generated calibration signal to offset or remove the groupdelay errors in the received GLONASS signals. Once GPS signals arepresent or become available for use, the combined GPS and GLONASSreceiver 120 may determine or calculate GPS navigation information fromthe received GPS signals for the combined GPS and GLONASS receiver 120.The determined GPS navigation information may be converted ortransformed to corresponding GLONASS navigation information to update orrefine the calibration coefficients of the calibration signal. Thecombined GPS and GLONASS receiver 120 may utilize the resulting updatedcalibration signal to continue the calibration of the received GLONASSsignals.

In instances where the combined GPS and GLONASS receiver 120 needs to beturned off or shut down, the combined GPS and GLONASS receiver 120 maybe configured to store the latest calibration coefficients of thecalibration signal and/or the latest group delay errors before turningoff. The combined GPS and GLONASS receiver 120 may utilize the storedcalibration coefficients or group delay errors to form or generate acalibration signal upon turning on. In this regard, the combined GPS andGLONASS receiver 120 may utilize the stored calibration coefficients orgroup delay errors to start the calibration of received GLONASS signalsimmediately upon turning on. The combined GPS and GLONASS receiver 120may incorporate subsequently received GPS signals and/or GLONASS signalsto update or refine the calibration coefficients to continue thecalibration of the subsequently received GLONASS signals.

Many applications such as car navigation, aircraft navigation, andscientific applications may benefit from use of both systems in the samesatellite receiver. A combined GPS and GLONASS receiver may provide ahigh degree of system-wide integrity. For example, if either the GPS orthe GLONASS suffers a system-wide failure then the combined GPS andGLONASS satellite receiver will continue to operate with the remainingGPS or GLONASS operational systems. When both the GPS system and theGLONASS systems are operational, measurements from each of them may becontinually compared in order to detect the system-wide failures. Thesystem-wide failure includes not only the satellite failing in somemanner, but also includes operating in environments where heavy radiofrequency interferences may be present. The radio interferencesaffecting one system need not affect the other system because GPS andGLONASS operate in different frequency bands. Code phase (also known aspseudo-range) measurements are commonly processed in combined GPS andGLONASS receivers to provide high accuracy position, velocity and timemeasurements. Depending on implementation, it may be desirable for acombined GPS and GLONASS receiver to include specific filter andamplifier components to prevent, for example, possible jamming. Thespecific characteristics of filters, amplifiers and other activecomponents in the combined GPS and GLONASS receiver design may causegroup delay distortion, which is the variations in group delay acrossthe received bandwidth, and may result in error in code phasemeasurements.

FIG. 2 is a diagram illustrating an exemplary combined GPS and GLONASSreceiver, in accordance with an embodiment of the invention. Referringto FIG. 2, there is shown a combined GPS and GLONASS receiver 120,comprising a receiver front end 210, a navigation processor 220, acalibration signal generator 230, and a signal calibrator 240. Thereceiver front end 210 may comprise a GPS front end 212 and a GLONASSfront end 214. The navigation processor 220 may comprise a processor 222and a memory 224. The combined GPS and GLONASS receiver 120 may becommunicatively coupled to the receiver antenna 130. Although a singleantenna is illustrated, the invention may not be so limited.Accordingly, one or more antennas may be utilized by the combined GPSand GLONASS receiver 120 without departing from the spirit and scope ofvarious embodiments of the invention.

The receiver front end 210 may comprise suitable logic, circuitry and/orcode that may be enabled to receive satellite broadcast signals via thereceiver antenna 130 and process them so as to generate basebandsignals, which may be suitable for further processing in the combinedGPS and GLONASS receiver 120.

The GPS front end 212 may comprise suitable logic, circuitry and/or codethat may be enabled to receive GPS satellite broadcast signals via thereceiver antenna 130 and convert them to GPS baseband signals, which maybe suitable for further processing in the combined GPS and GLONASSreceiver 120 for navigation information, whether GPS based or combinedGPS and GLONASS based.

The GLONASS front end 214 may comprise suitable logic, circuitry and/orcode that may be enabled to receive GLONASS satellite broadcast signalsvia the receiver antenna 130 and convert them to GLONASS basebandsignals, which may be suitable for further processing in the combinedGPS and GLONASS receiver 120 for navigation information, whether GLONASSbased or combined GPS and GLONASS based.

The navigation processor 220 may comprise suitable logic, circuitryand/or code that may be enabled to process received satellite signalsvia the receiver front end 210 and extract information for each receivedsatellite signal to provide navigation information for the combined GPSand GLONASS receiver 120.

The processor 222 may comprise suitable logic, circuitry and/or codethat may be operable to determine navigation information from thereceived satellite signals that are processed by the correspondingGLONASS front end 210 and GPS front end 212. The navigation informationmay be a GPS based or a GLONASS based. The processor 222 may use variousalgorithms to combine the GPS based information and the GLONASS basednavigation information into combined navigation information. Thecombined navigation information may be generated by removing errors suchas the group delay error from the received GLONASS signals based on theGPS based navigation information. In this regard, the processor 222 maybe operable to start the calibration of the received GLONASS signalsbefore GPS signals become available for use. In other words, theprocessor 222 may also be operable to remove or offset the group delayerror in the received GLONASS signals without utilizing the GPS basednavigation information.

In an exemplary embodiment of the invention, in instances when GPSsignals are not available for use, the processor 222 may be operable toobtain group delay errors from the received GLONASS signals to estimateor determine group delay variations for GLONASS channels. The processor222 may also be operable to obtain group delay errors that are stored ina look-up table, for example, inside the memory 224 to estimate ordetermine group delay variations for GLONASS channels. The processor 222may utilize the determined group delay variations as calibrationcoefficients to form or generate a calibration signal. In this regard,the generated calibration signal is reflective of the determined groupdelay variations. The processor 222 may utilize the generatedcalibration signal to remove or offset the group delay errors in thereceived GLONASS signals. Once GPS signals are present or becomeavailable for use, the processor 222 may incorporate the GPS signals tocalibrate the received GLONASS signals by offsetting the associatedgroup delay errors. The processor 222 may be operable to store thelatest group delay variations or calibration coefficients before thecombined GPS and GLONASS receiver 120 is turned off. The processor 222may utilize the stored calibration coefficients to form or generate acalibration signal to start the calibration of GLONASS signals receivedupon turning on the combined GPS and GLONASS receiver 120.

The memory 224 may comprise suitable logic, circuitry, and/or code thatenable storing information such as executable instructions and data thatmay be utilized by the processor 222. The executable instructions maycomprise algorithms that may be enabled to calculate navigationinformation using the acquired satellite signals automatically or uponrequest/signaled. The data may comprise a calibration signal comprisingvarious calibration coefficients that may be used for calibrating thereceived GLONASS signals. The memory 224 may comprise RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage.

The calibration signal generator 230 may comprise suitable logic,circuitry, and/or code that may enable generation of a calibrationsignal, comprising plurality of calibration coefficients. Thecalibration signal generator 230 may convert GPS based navigationinformation into corresponding GLONASS navigation information. Anexpected GLONASS signal associated with the corresponding GLONASSnavigation information may be estimated. The expected GLONASS signalsmay be compared to the actual received GLONASS signals at thecalibration signal generator 230 to determine group delay errors foreach received GLONASS signal. These group delay errors may be used ascalibration coefficients of the generated calibration signal to becommunicated to the signal calibrator 240 to calibrate the receivedGLONASS signals by dynamically removing or offsetting correspondinggroup delay errors in the received GLONASS signals.

In instances where GLONASS signals are received before GPS signals arepresent or become available for use, the calibration signal generator230 may learn or obtain the group delay errors in the received GLONASSsignals to estimate calibration coefficients of the calibration signal.In some instances, group delay errors may be previously stored insidethe memory 224, the calibration signal generator 230 may be operable toobtain the stored group delay errors from the memory 224 to determine orestimate calibration coefficients of the calibration signal. Theresulting calibration signal may be utilized to offset the group delayerrors in the received GLONASS signals. Once GPS signals are present orbecome available for use, the calibration signal generator 230 mayincorporate the GPS signals into the calibration of the received GLONASSsignals.

In some instances, the combined GPS and GLONASS receiver 120 may need tobe turned off. In this regard, the combined GPS and GLONASS receiver 120may store the latest calibration coefficients into a look-up table, forexample, inside the combined GPS and GLONASS receiver 120 before turningoff. Once the combined GPS and GLONASS receiver 120, is turned on, thecalibration signal generator 230 may utilize the stored calibrationcoefficients to generate a calibration signal to immediately start thecalibration of GLONASS signals received. The stored calibrationcoefficients may be updated or refined utilizing the received GLONASSsignals to continue the calibration process for the subsequentlyreceived GLONASS signals.

The signal calibrator 240 may comprise suitable logic, circuitry, and/orcode that may be configured to remove associated group delay errors fromthe received GLONASS signals by combining the received GLONASS signalswith a calibration signal from the calibration signal generator 230. Thesignal calibrator 240 may communicate the calibrated GLONASS signalswith the navigation processor 220 to produce GLONASS based navigationinformation or combined GPS and GLONASS based navigation information.

In operation, a plurality of satellite signals from GPS satellites suchas 110 a and 110 b, and GLONASS satellites such as 110 c and 110 d maybe received at the antenna 130 of the combined GPS and GLONASS receiver120. The combined GPS and GLONASS receiver 120 may be enabled toidentify and determine the satellite source for each satellite signal.Depending on the type of received satellite signals, the receivedsatellite signals may be measured at the antenna 130 and communicated tothe GPS front end 212 or the GLONASS front end 214, respectively. Thereceived GPS signals may be demodulated and converted to basebandsignals via the GPS front end 212 and communicated to the navigationprocessor 220. The processor 222 in the navigation processor 220 may usevarious algorithms stored in the memory 224 to calculate GPS navigationinformation for the combined GPS and GLONASS receiver 120. The resultingGPS navigation information may be communicated to the calibration signalgenerator 230. The calibration signal generator 230 may be operable toestimate the GLONASS signals based on the GPS based navigationinformation. The estimated GLONASS signals may be compared to the actualGLONASS signals at the calibration signal generator 230. The resultingerrors such as group delay errors for each of the GLONASS signals may bedetermined. These group delay errors may be used to generate acalibration signal, which may be communicated to the signal calibrator240. In this regard, in instances where GLONASS signals are receivedbefore GPS signals are present for use, the calibration signal generator230 may learn or obtain group delay variations from the group delayerrors in the received GLONASS signals and/or from group delay errorspreviously stored in the memory 224. The calibration signal generator230 may utilize the obtained group delay variations to immediately startthe calibration of the received GLONASS signals without use of GPSsignals. The signal calibrator 240 may be operable to calibrate, in realtime, the received GLONASS signals by offsetting the group delay errorsin GLONASS signals.

FIG. 3 is a diagram illustrating an exemplary calibration signalgenerator, in accordance with an embodiment of the invention. Referringto FIG. 3, there is shown a calibration signal generator 230 comprisinga time transfer 302, a signal estimator 304, and a signal comparator306.

The time transfer 302 may comprise suitable logic, circuitry, and/orcode that may enable taking a receiver clock offset determined by a GPSbased navigation solution and adding GPS-GLONASS system time referencebias to it.

The signal estimator 304 may comprise suitable logic, circuitry, and/orcode that may enable estimation of GLONASS signals corresponding togiven navigation information. The clock information associated to theestimated GLONASS signals may be the transferred receiver clock offsetfrom the time transfer 302.

The signal comparator 306 may comprise suitable logic, circuitry, and/orcode that may enable comparing the estimated GLONASS signals with actualreceived GLNASS signals to generate, for example, group delay errors foreach received GLONASS signal. The resulting group delay errors may beoutputted as calibration coefficients to the signal calibrator 240.

In operation, GPS based navigation information for the combined GPS andGLONASS receiver 120 may be calculated by the navigation processor 220based on the demodulated received GPS signals and pass to thecalibration signal generator 230. The clock information associated withthe GPS based navigation information may be extracted at the timetransfer 302 and may be transferred to a corresponding GLONASS receiverclock offset from the GLONASS satellite system. The signal estimator 304may estimate respective GLONASS signals corresponding to the GPSnavigation information with the transferred GLONASS receiver clockoffset. The signal comparator 306 may compare each of the receivedGLONASS signal with the respective estimated GLONASS signal. Based onthe comparison, corresponding group delay errors may be generated by thesignal comparator 306 for each received GLONASS signal. Thecorresponding generated group delay errors may be outputted as acalibration signal from the calibration signal generator 230 andutilized to calibrate the group delay errors for the received GLONASSsignals.

FIG. 4 is a diagram illustrating an exemplary error state Kalman filterused in a combined GPS and GLONASS receiver, in accordance with anembodiment of the invention. Referring to FIG. 4, there is shown asignal calibrator 240, comprising an error state Kalman filter 402 and asignal coupler 404.

The signal calibrator 240 may comprise suitable logic, circuitry, and/orcode that may be operable to improve or optimize the accuracy ofreceived GLONASS signals by removing associated group delay errors.

The error state Kalman filter 402 may comprise suitable logic,circuitry, and/or code that may be configured to provide an optimizedestimate of group delay variations in received GLONASS signals at thecombined GPS and GLONASS receiver 120 in real time. The error stateKalman filter 402 may indicate how quickly the group delay variations inthe received GLONASS signals may stabilize. The error state Kalmanfilter 402 may produce an adaptive adjustment to be used for offsettingthe group delay variations in the received GLONASS signals. Error statesassociated with the error state Kalman filter 402 may be defined and maycomprise group delay errors from each received GLONASS signal at thecombined GPS and GLONASS receiver 120. Initially the group delay errorsmay be substantially unknown and may be estimated to be zero, forexample. This may indicate that the error state Kalman filter 402 maymake little use of GLONASS measurements for navigation. As the filteringprocess may continue, the group delay errors may become known, the errorstate Kalman filter 402 may make substantially use of the GLONASSmeasurements for navigation. In other words, as the filtering processmay continue, the estimated group delay variations associated with thereceived GLONASS signals may become stable, that is, bounded within anacceptable range. In this regard, the error state Kalman filter 402 maymake substantially use of the GLONASS measurements to produce orgenerate navigation information for the combined GPS and GLONASSreceiver 120.

The error state Kalman filter 402 may ensure gradual changes in thegroup delay errors. The error state Kalman filter 402 may continuouslyupdate the calibration coefficients while simultaneously making use ofthem.

The signal coupler 404 may comprise suitable logic, circuitry, and/orcode that may be operable to combine the actual received GLONASS signalwith estimated group delay variations from the error state Kalman filter402 in order to produce respective calibrated GLONASS signals. The groupdelay errors in the received GLONASS signals may be offset and/orremoved by the signal coupler 404. The signal coupler 404 may beoperable to communicate the calibrated GLONASS signals to the navigationprocessor 220 in the combined GPS and GLONASS receiver 120. Theprocessor 222 may utilize the calibrated GLONASS signals to generateGLONASS related navigation information.

The error state Kalman filter 402 may be implemented in various wayswithout departing from the scope of the various embodiments of theinvention. For example, the calibration information from the error stateKalman filter 402 may be applied outside the error state Kalman filter402 as described with respect to FIG. 4. The calibration information mayalso be fed back to the error state Kalman filter 402 for computing asolution.

Although a single error state Kalman filter 402 is illustrated, theinvention may not be so limited. Accordingly, one or more error stateKalman filters may be utilized by the combined GPS and GLONASS receiver120 without departing from the spirit and scope of various embodimentsof the invention.

FIG. 5 is a flow chart illustrating exemplary steps for calibratinggroup delay errors in a combined GPS and GLONASS receiver, in accordancewith an embodiment of the invention. Referring to FIG. 5, the exemplarysteps may begin with step 502, where the combined GPS and GLONASSreceiver 120 may select satellites for tracking. In step 510, thecombined GPS and GLONASS receiver 120 may start taking measurements forthe received GPS signals from the corresponding GPS satellites. In step512, the combined GPS and GLONASS receiver 120 may extract navigationinformation from the received GPS signals. The extracted navigationinformation may be communicated to the navigation processor 220 toproduce a GPS based navigation information for the combined GPS andGLONASS receiver 120, the process may proceed in step 510 and/or step522.

In step 520, the combined GPS and GLONASS receiver 120 may start takingmeasurements for the received GLONASS signals from the correspondingGLONASS satellites. In step 522, it may be determined whether thereceived GLONASS signals should be calibrated. In instances where thereceived GLONASS signals may need to be calibrated for offsettingvariations in associated group delay errors, then in step 524, theGLONASS signals may be estimated based on the GPS based navigationinformation calculated in step 512. In step 526, a calibration signalcomprising calibration coefficients for calibrating the received GLONASSsignals may be generated. In step 528, the received GLONASS signals maybe calculated based on the generated calibration signal. In step 530,navigation information from the calibrated GLONASS signals may beextracted and GLONASS based navigation information may be determinedbased on the calibrated GLONASS signals. The exemplary steps may thenreturn to step 520. In step 522, in instances where the received GLONASSsignals may not need to be calibrated, then in step 530, GLONASSnavigation information may be determined based on the actual receivedGLONASS signals. The exemplary steps may then return to step 520.

FIG. 6 is a flow chart illustrating exemplary steps for offsetting groupdelay errors in a combined GPS and GLONASS receiver, in accordance withan embodiment of the invention. Referring to FIG. 6, the exemplary stepsmay begin with step 602, where the combined GPS and GLONASS receiver 120may track or select GPS and GLONASS satellites. GLONASS signals arepresent and received from corresponding GLONASS satellites. In step 604,the combined GPS and GLONASS receiver 120 may start taking measurementsfor the received GLONASS signals. In step 606, it may be determinedwhether GPS signals are present for use by the combined GPS and GLONASSreceiver 120. In instances where GPS signals are not present oravailable for use by the combined GPS and GLONASS receiver 120, then instep 608, in which the combined GPS and GLONASS receiver 120 maydetermine or extract GLONASS navigation information from the GLONASSmeasurements. In step 610, the combined GPS and GLONASS receiver 120 maydetermine or estimate calibration coefficients (group delay variations)from the GLONASS navigation information. In instances where group delayerrors in terms of GLONASS channels are previously stored into thecombined GPS and GLONASS receiver 120 by manufacturer or receiverdesigners, the combined GPS and GLONASS receiver 120 may determine orestimate calibration coefficients (group delay variations) utilizing thestored group delay errors. Once GPS signals are present or becomeavailable for use, the combined GPS and GLONASS receiver 120 mayincorporate corresponding GPS based navigation information to determineor estimate calibration coefficients (group delay variations). In step612, the calibration signal generator 230 may utilize the estimatedcalibration coefficients to form or generate a calibration signal. Instep 614, the signal calibrator 240 may utilize the generatedcalibration signal to offset the group delay errors in the receivedGLONASS signals for the calibration of the received GLONASS signals. Instep 616, the navigation processor 220 may calculate or determine aGLONASS based navigation solution utilizing the calibrated GLONASSsignals.

In step 606, in instances where GPS signals are present or available foruse by the combined GPS and GLONASS receiver 120, then in step 618, inwhich the combined GPS and GLONASS receiver 120 may start takingmeasurements for the received GPS signals. In step 620, the combined GPSand GLONASS receiver 120 may determine or extract GPS navigationinformation from the GPS measurements. In step 622, the combined GPS andGLONASS receiver 120 may convert the determined GPS based navigationinformation to corresponding GLONASS navigation information. Theexemplary steps may proceed in step 610.

FIG. 7 is a flow chart illustrating exemplary steps for immediatelyoffsetting group delay errors in a combined GPS and GLONASS receiverupon turning on, in accordance with an embodiment of the invention.Referring to FIG. 7, the exemplary steps may begin with step 702, wherethe combined GPS and GLONASS receiver 120 may calibrate received GLONASSsignals utilizing a calibration signal. In step 704, the navigationprocessor 220 may calculate or determine a GLONASS based navigationsolution utilizing the calibrated GLONASS signals. In step 706, it maybe determined whether the combined GPS and GLONASS receiver 120 needs tobe shout down or turned off. In instances where the combined GPS andGLONASS receiver 120 needs to be shut down, then in step 708, in whichthe combined GPS and GLONASS receiver 120 may store the latestcalibration coefficients of the calibration signal into the memory 224.In step 710, the combined GPS and GLONASS receiver 120 may be shut downafter the storage of the latest calibration coefficients. In step 712,it may be determined whether the combined GPS and GLONASS receiver 120needs to be turned on. In instances where the combined GPS and GLONASSreceiver 120 needs to be turned on, then in step 714, in which thecombined GPS and GLONASS receiver 120 is turned on. In step 716, thecalibration signal generator 230 may be operable to generate acalibration signal utilizing the stored calibration coefficients. Theexemplary steps may return to step 702.

In step 706, in instances where the combined GPS and GLONASS receiver120 does not need to be shut down, then the exemplary steps may returnto step 702. In step 712, in instances where the combined GPS andGLONASS receiver 120 does not need to be turned on, then the exemplarysteps may stay in step 712.

Aspects of a method and system for calibrating group delay errors in acombined GPS and GLONASS receiver are provided. In accordance withvarious embodiments of the invention, the combined GPS and GLONASSreceiver 120 may be operable to receive a plurality of GPS signals and aplurality of GLONASS signals. A calibration signal may be generatedutilizing the received GPS signals and/or the received GLONASS signals.The combined GPS and GLONASS receiver 120 may utilize the generatedcalibration signal to offset group delay errors in one or more of theplurality of received GLONASS signals. The generated calibration signalmay be processed or filtered through one or more Kalman filters such asthe error state Kalman filter 402 before calibrating the receivedGLONASS signals. The filtered calibration signal that is reflective ofor corresponds to the group delay variations associated with thereceived GLONASS signals. The group delay variations may be estimatedvia the Kalman filtering. The estimated group delay variations may becombined with the received GLONASS signals. In this regard, theestimated group delay variations may be offset to calibrate the receivedGLONASS signals. The resulting calibrated received GLONASS signals maybe utilized by the combined GPS and GLONASS receiver 120 to generateGLONASS related navigation information. In instances where the estimatedgroup delay variations are stable, the combined GPS and GLONASS receiver120 may also be operable to directly utilize, the received GLONASSsignals to generate GLONASS related navigation information.

In some circumstances, the combined GPS and GLONASS receiver 120 mayreceive the GLONASS signals before the GPS signals are present or becomeavailable for use. In this regard, the combined GPS and GLONASS receiver120 may be operable to determine or estimate group delay variations,namely, calibration coefficients, before the GPS signals becomeavailable for use. For example, the combined GPS and GLONASS receiver120 may be operable to collect or obtain the group delay, errors in thereceived GLONASS signals. The combined GPS and GLONASS receiver 120 maydetermine or estimate calibration coefficients based on the obtainedgroup delay errors. In another example, in instances where group delayerrors for various GLONASS channels are stored in a look-up table, forexample, inside the memory 224, the combined GPS and GLONASS receiver120 may be operable to obtain or read the stored group delay errors fromthe look-up table in the memory 224. The combined GPS and GLONASSreceiver 120 may determine or estimate calibration coefficients based onthe obtained stored group delay errors. Once the GPS signals arereceived by the combined GPS and GLONASS receiver 120, the estimatedcalibration coefficients may be updated or refined based on the receivedGPS signals. For example, the combined GPS and GLONASS receiver 120 maydetermine or calculate GPS based navigation information from thereceived GPS signals. The determined GPS based navigation informationmay be converted into corresponding GLONASS based navigation informationto update or refine the estimated calibration coefficients (group delayvariations). The combined GPS and GLONASS receiver 120 may be operableto utilize the updated calibration coefficients to form or generate thecalibration signal for the calibration of the received GLONASS signals.

In some instances, the combined GPS and GLONASS receiver 120 may beturned on or off. In this regard, before turning off the combined GPSand GLONASS receiver 120, the updated calibration coefficients may bestored into the memory 224. The stored calibration coefficients may beutilized to expedite the calibration of received GLONASS signals uponturning on the combined GPS and GLONASS receiver 120. More specifically,the combined GPS and GLONASS receiver 120 may be operable to generate acalibration signal utilizing the stored calibration coefficients uponturning on. The combined GPS and GLONASS receiver 120 may immediatelycalibrate received GLONASS signals, upon turning on, utilizing thegenerated calibration signal. In instances where the GLONASS signals arereceived without the presence of GPS signals, the combined GPS andGLONASS receiver 120 may collect or obtain the group delay errors in thereceived GLONASS signals to update or refine the generated calibrationsignals for the calibration of the received GLONASS signals. Once GPSsignals are present and become available for use, the combined GPS andGLONASS receiver 120 may update the calibration signal utilizing thereceived GPS signals to continue calibrating of the received GLONASSsignals.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein for calibratinggroup delay errors in a combined GPS and GLONASS receiver.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method of processing signals, the method comprising: in a combinedGPS and GLONASS receiver: receiving a plurality of GPS signals and aplurality of GLONASS signals; generating a calibration signal utilizingsaid received plurality of GPS signals and/or said received plurality ofGLONASS signals; and offsetting group delay errors in one or more ofsaid received plurality of GLONASS signals utilizing said generatedcalibration signal.
 2. The method according to claim 1, comprising:filtering said generated calibration signal; and offsetting said groupdelay errors in said one or more of said received plurality of GLONASSsignals utilizing said filtered calibration signal.
 3. The methodaccording to claim 2, comprising filtering said generated calibrationsignal via one or more Kalman filters.
 4. The method according to claim2, wherein said filtered generated calibration signal comprises groupdelay variations associated with said received plurality of GLONASSsignals.
 5. The method according to claim 4, comprising estimating saidgroup delay variations associated with said received plurality ofGLONASS signals via said filtering.
 6. The method according to claim 5,comprising offsetting said estimated group delay variations in said oneor more of said received plurality of GLONASS signals.
 7. The methodaccording to claim 6, comprising combining said one or more of saidreceived plurality of GLONASS signals with said estimated group delayvariations for said offsetting.
 8. The method according to claim 7,comprising calibrating said one or more of said received plurality ofGLONASS signals via said combining.
 9. The method according to claim 8,comprising generating GLONASS related navigation information utilizingsaid calibrated one or more of said received plurality of GLONASSsignals.
 10. The method according to claim 5, comprising generatingGLONASS related navigation information utilizing said one or more ofsaid received plurality of GLONASS signals based on said estimated groupdelay variations.
 11. The method according to claim 4, comprisingestimating said group delay variations associated with said receivedplurality of GLONASS signals prior to said receiving of said pluralityof GPS signals.
 12. The method according to claim 11, comprising:obtaining said group delay errors in said received plurality of GLONASSsignals; and estimating said group delay variations based on saidobtained group delay errors in said received plurality of GLONASSsignals.
 13. The method according to claim 11, comprising: obtaininggroup delay errors that are previously stored inside said combined GPSand GLONASS receiver; and estimating said group delay variations basedon said obtained stored group delay errors.
 14. The method according toclaim 11, comprising: generating said calibration signal utilizing saidestimated group delay variations; and offsetting said group delay errorsin said one or more of said received plurality of GLONASS signalsutilizing said generated calibration signal.
 15. The method according toclaim 11, comprising updating said estimated group delay variationsutilizing a plurality of subsequently received GPS signals.
 16. Themethod according to claim 15, comprising: generating an updatedcalibration signal utilizing said updated estimated group delayvariations; and offsetting said group delay errors in one or more of aplurality of subsequently received GLONASS signals utilizing saidupdated calibration signal.
 17. The method according to claim 16,comprising storing said updated estimated group delay variations beforesaid combined GPS and GLONASS receiver is turned off.
 18. The methodaccording to claim 17, comprising: generating an updated calibrationsignal utilizing said stored group delay variations when said combinedGPS and GLONASS receiver is turned on; and calibrating one or moreGLONASS signals, which are received after said combined GPS and GLONASSreceiver is turned on, utilizing said generated updated calibrationsignal.
 19. The method according to claim 18, comprising: updating saidstored group delay variations, so as to generate a newly updatedcalibration signal, utilizing said one or more GLONASS signals and/orone or more GPS signals, which are received after said combined GPS andGLONASS receiver is turned on; and calibrating said one or more GLONASSsignals, which are received after said combined GPS and GLONASS receiveris turned on, utilizing said generated newly updated calibration signal.20. A system for processing signals, the system comprising: one or morecircuits for use in a combined GPS and GLONASS receiver, said one ormore circuits being operable to: receive a plurality of GPS signals anda plurality of GLONASS signals; generate a calibration signal utilizingsaid received plurality of GPS signals; and offset group delay errors inone or more of said received plurality of GLONASS signals utilizing saidgenerated calibration signal.
 21. The system according to claim 20,wherein said one or more circuits are operable to filter said generatedcalibration signal; and offset said group delay errors in said one ormore of said received plurality of GLONASS signals utilizing saidfiltered calibration signal.
 22. The system according to claim 21,wherein: said one or more circuits comprise one or more Kalman filters;and said one or more Kalman filters are operable to filter saidgenerated calibration signal.
 23. The system according to claim 21,wherein said filtered generated calibration signal comprises group delayvariations associated with said received plurality of GLONASS signals.24. The system according to claim 23, wherein said one or more circuitsare operable to estimate said group delay variations associated withsaid received plurality of GLONASS signals via said filtering.
 25. Thesystem according to claim 24, wherein said one or more circuits areoperable to offset said estimated group delay variations in said one ormore of said received plurality of GLONASS signals.
 26. The systemaccording to claim 25, wherein said one or more circuits are operable tocombine said one or more of said received plurality of GLONASS signalswith said estimated group delay variations for said offsetting.
 27. Thesystem according to claim 26, wherein said one or more circuits areoperable to calibrate said one or more of said received plurality ofGLONASS signals via said combining.
 28. The system according to claim27, wherein said one or more circuits are operable to generate GLONASSrelated navigation information utilizing said calibrated one or more ofsaid received plurality of GLONASS signals.
 29. The system according toclaim 24, wherein said one or more circuits are operable to generateGLONASS related navigation information utilizing said one or more ofsaid received plurality of GLONASS signals based on said estimated groupdelay variations.
 30. The system according to claim 23, wherein said oneor more circuits are operable to estimate said group delay variationsassociated with said received plurality of GLONASS signals prior to saidreceiving of said plurality of GPS signals.
 31. The system according toclaim 30, wherein said one or more circuits are operable to obtain saidgroup delay errors in said received plurality of GLONASS signals; andestimate said group delay variations based on said obtained group delayerrors in said received plurality of GLONASS signals.
 32. The systemaccording to claim 30, wherein said one or more circuits are operable toobtain group delay errors that are previously stored inside saidcombined GPS and GLONASS receiver; and estimate said group delayvariations based on said obtained stored group delay errors.
 33. Thesystem according to claim 30, wherein said one or more circuits areoperable to generate said offset said group delay errors in said one ormore of said received plurality of GLONASS signals utilizing saidgenerated calibration signal.
 34. The system according to claim 30,wherein said one or more circuits are operable to update said estimatedgroup delay variations utilizing a plurality of subsequently receivedGPS signals.
 35. The system according to claim 30, wherein said one ormore circuits are operable to generate an updated calibration signalutilizing said updated estimated group delay variations; and offset saidgroup delay errors in one or more of a plurality of subsequentlyreceived GLONASS signals utilizing said updated calibration signal. 36.The system according to claim 35, wherein said one or more circuits areoperable to store said updated estimated group delay variations beforesaid combined GPS and GLONASS receiver is turned off.
 37. The systemaccording to claim 36, wherein said one or more circuits are operable togenerate an updated calibration signal utilizing said stored group delayvariations when said combined GPS and GLONASS receiver is turned on; andcalibrate one or more GLONASS signals, which are received after saidcombined GPS and GLONASS receiver is turned on, utilizing said generatedupdated calibration signal.
 38. The system according to claim 37,wherein said one or more circuits are operable to update said storedgroup delay variations, so as to generate a newly updated calibrationsignal, utilizing said one or more GLONASS signals and/or one or moreGPS signals, which are received after said combined GPS and GLONASSreceiver is turned on; and calibrate said one or more GLONASS signals,which are received after said combined GPS and GLONASS receiver isturned on, utilizing said generated newly updated calibration signal.